Wireless communication systems, such as cellular telephone systems, have proved to be very popular. Such systems typically include numerous mobile units (e.g., cellular telephones), a plurality of base stations at fixed locations, and one or more switching centers connecting the wireless communication systems to other communications systems, such as the land line public switched telephone network.
It is common for such systems to employ a large number of discrete communication channels for communicating voice and data from one location to another and for controlling system functions. It is also common for there to be multiple communications service providers in competition with each other for each type of communication service. As such, within a given geographical area it is typical for the various communication channels to be allocated to the different competitors such that only one service provider is responsible for providing service on any given channel.
To facilitate communications channel allocation, the spectrum of channels may be divided into several channel bands, each containing a plurality of communications channels. Thereafter, an entire channel band may be allocated to a particular service provider for a given geographic region. Thus, in a certain region, service provider Alpha may be allocated channel bands A and C, while service provider Beta may be allocated channel band B, and service provider Gamma all other channel bands. The particular details of the channel band allocations are well known in the industry. Further, because it is desirable for a subscriber of service provider Alpha to use service provider Alpha's communications channels, it is common for mobile units subscribing to Alpha's service to maintain a listing of the channel bands allocated to Alpha. This list is then used to preferentially select which channels are used for communications.
During use, it is common for the mobile unit to be switched from one channel to another, an event which can be triggered by a wide variety of reasons. For example, in a cellular phone call release procedure, a cellular base station can provide a channel pointer that will direct a mobile cellular phone to switch to a new control channel to await future paging signals. As another example, a mobile unit may receive a channel pointer as part of a redirection procedure to alleviate overload conditions when a base station is handling too many communications sessions. In any event, because it is very desirable for channel switching to be transparent to the user, this channel switching must happen as quickly as possible. In addition, because the channel switching utilizes system resources including mobile unit power, the switching procedure should be as efficient as possible.